1. Technical Field
This invention is related to the field of automobile ignition diagnostic systems. More particularly, it is related to the field of supplying power to an ionization detection circuit.
2. Discussion
In a spark ignition (SI) engine, the spark plug is inside of the combustion chamber and can be used as a detection device without requiring the intrusion of a separate sensor. Many ions are produced in the plasma during combustion of an engine. For example, H3O+, C3H3+, and CHO+ are produced by the chemical reactions at the flame front and have sufficiently long excitation time to be detected. In addition, a voltage applied across the spark gap attracts free ions and creates an ionization current.
The prior art includes a variety of conventional methods for detecting and using ionization current in a combustion chamber of an internal combustion engine. However, each of the various conventional systems suffers from a great variety of deficiencies.
A typical ionization detector consists of a coil-on-plug arrangement, with a device in each coil to keep a voltage applied across the spark plug electrodes when the spark is not arcing. The current across the spark plug electrodes is isolated prior to being measured. There are two ways to supply regulated power to an in-cylinder ionization detector. A first approach is to use a charge pump powered by a DC power supply such as a battery. A second approach is to use a charge pump powered by ignition flyback energy. The DC power supply and the ignition flyback energy generate a DC bias used by the charge pump to detect ionization current.
Both approaches present disadvantages. A DC power supply is many times too large due to large high-voltage electronics. The flyback energy approach requires a few ignition events to obtain a regulated power supply. This is undesirable for cylinder identification, since cylinder identification uses a regulated power supply at the first ignition event. In addition, the high voltage capacitors used with the flyback energy approach tend to be unreliable due to the high voltage and the high operational temperature.